Printing machines with printing couples which include a plate cylinder and a blanket, typically rubber blanket cylinder, and in which the printing couples are generally in Y-shaped configuration, are known. The cylinders of the printing machines are driven via gears, coupled to shafts of the printing machines are driven via gears, coupled to shafts on the cylinders. The gears, when formed as inclined or spiral gears, provide for good meshing; upon axial shifting of any one of the cylinders, the spiral engagement of the gears will also cause rotation of the cylinders. The gears are in continuous meshing engagement, and all the cylinders are axially shiftable. Drive power to the cylinders of the three printing couples is obtained from a drive pinion, coupled to the main power drive of the machine. The drive pinion, likewise, has spiral teeth. It may be considered to define a fixed or reference circumferential rotary position since, upon axial shifting of an engaged cylinder, the engaged cylinder will also rotate with respect to the drive pinion.
It is known to change the register of printing machine cylinders by shifting the printing machine cylinders axially. Depending on the angle of inclination, axial shifting of any one of the cylinders will, necessarily, result in a rotary shift of the respective cylinders. Axial register adjustment, thus, may result in rotary misalignment. It is then necessary to compensate for the rotary shift if only axial register is to be changed. This, of course, is time-consuming and difficult to carry out. Clutches can be used interposed between the cylinders in the respective gear wheels, or the gears themselves may be shiftable or slidable on the shafts coupled to the cylinders, or stub shafts, integral therewith. This somewhat simplifies change of register and permits less time-consuming adjustment of register, but requires substantial structural equipment and, hence, is expensive.